The longitudinal dimension of laser speckle was measured in the near field of a uniformly illuminated frosted-glass diffuser. Theory indicates that the speckle produced by the circular spot varies according to XL2/D2, where X is the wavelength of the laser, L is the distance from the observation position to the diffuser, and D is the diameter of the illuminated spot. A single wavelength was used, allowing variation with respect to L and D to be measured. The experimental results obtained closely match the theory. More than 400 speckle lengths were measured, normalized by multiplying by D2/L2, and statistically analyzed to deter-mine a mean of 11µm and a standard deviation of 2.5µm.
C. E. Halford,
W. L. Gamble,
"Experimental Investigation Of The Longitudinal Characteristics Of Laser Speckle," Optical Engineering 26(12), 261263 (1 December 1987). http://dx.doi.org/10.1117/12.7977166